In accordance with reduction of a product cycle as well as a tendency of increasing the types of products and decreasing the quantity of products of each type, demands for inexpensive dies having a resin core and/or a resin cavity block which can comply with them have been increased in recent years. In the prior art, the resin core and/or resin cavity block are manufactured in such a manner that one prepare a master model of wood or the like which corresponds to a part or product to be molded, and using this model as an inner core, thermosetting resin such as epoxy resin or urethane resin is molded into an intended form by casting, defoaming and curing the same.
For manufacturing the dies having the resin core, cavity block or the like made of resin, the master model is essential. However, production of the master model requires a complicated work.
The thermosetting resin such as epoxy resin or urethane resin is used as the material for molding dies, because it is liquid in the room temperature and hence can be easily casted. However, in order to prevent mixing of bubbles during the casting, vacuum deaeration and curing take a long time, and cure shrinkage occurs, so that it is difficult to achieve an intended size accuracy. Further, even if one intends to recycle the resin core, cavity block and others of the die by pulverizing them after the use thereof, recycling of the used dies is impossible, because the property is deteriorated than intended property.
In order to overcome the problem relating to the recycle of the dies made of the thermosetting resin, it may be envisaged to prepare dies made of thermoplastic resin. In general, however, the thermoplastic resin has a very high viscosity, so that a pressure must be applied during casting, and the resin may not be supplied into a minute space even by the pressure, which make it impossible to reproduce a minute irregularity or the like on the master model.
Japanese Laid-Open Patent Publication No. 51-119765 (1976) discloses a die which is made of thermoplastic resin containing inorganic fibers such as glass fibers, or inorganic powder material such as calcium carbonate or river sand, and is used for contact-pressure molding of reinforced plastics. However, this die is manufactured by injection molding or compression molding, and requires a master model for forming the die.
For example, in the injection molding of resin, design of the product and design of the die have peculiarity distinguishing them from general part design. Thus, even if a designer completes the design of a product by determining numerical data of a specific configuration of the product and preparing the drawings, manufacturing of the resin product cannot be started immediately. When the product design is completed, it is then necessary to design the molding dies which are transferring tools for manufacturing the product. Whenever the new design of the resin product is employed, new dies must be manufactured. Further, the products manufactured with the dies cannot be directly repaired or modified, so that the dies (particularly, their core and cavity block) are required to have an extremely high accuracy.
In the prior art, the dies are generally made of metal. However, manufacturing of the dies made of metal, which require an extremely high accuracy as described above, requires a huge cost and a long term, which significantly impedes development of resin products. In particular, a tendency of increasing the types of products and decreasing the quantity of products of each type in the present time, which is contrary to the tendency of manufacturing a large quantity of products of a few types in the past, results in significant increase in number of the dies required for trial, evaluation and final production. In the process of designing a new product, such a situation is inevitable that the design of the product and hence the design of the die must be changed for changing a configuration, improving a function and reducing a product cost. Therefore, it is strongly desired to reduce the cost for manufacturing the die. Moreover, the product cycle has been remarkably reduced, so that it is very important to reduce a term required for manufacturing the die.
In view of the above, there have been various proposals. For example, the metal die is made of steel having a good machinability. The materials and parts of dies are standardized. The dies have a cassette type structure, in which only portions forming a cavity block and a core are exchangeable. Computers are used to improve the efficiency in die designing.
According to all the above proposals, however, the core and cavity block of the dies are made of metal, as is done in the conventional technique, and sufficient improvement cannot be achieved.
Accordingly, it is an object of the invention to provide a resin compound for a molding die, which does not require a master model, and allows machining for finishing a core, a cavity block or the like of the dies having a good dimensional accuracy and a high durability with a low cost and within a short term.
Another object of the invention is to provide a molding die having a part such as a core or a cavity block made of resin which can be recycle by pulverization thereof.
Still another object of the invention is to provide a molding die, which allows machining for finishing a core, a cavity block or the like having a good dimensional accuracy and a high durability with a low cost and within a short term, and hence can be entirely manufactured with a low cost and within a short term while maintaining a required accuracy.
Yet another object of the invention is to provide a method of molding of material such as resin which can provide an accurate and inexpensive molded product.